Toxoplasma gondii is a single-celled parasitic protozoan that infects and replicates in macrophages. It is common in the environment, and is transmitted to humans by the ingestion of undercooked meat or by accidental ingestion of the parasite's oocytes from contaminated water or cat litter. Infected individuals with healthy immune systems are generally asymptomatic, and rapidly clear the infection. However, in AIDS patients, infections of Toxoplasma gondii can lead to severe disease and even death. To investigate the immune mechanisms important in controlling Toxoplasma gondii, a mouse model of the infection was developed. Mice were infected with the protozoa at a dose where the majority of the mice survive the infection, and at the same time, were injected with a neutralizing antibody to a cytokine made by T cells (anti-'X' IgG). A second group of mice received the protozoa plus a control IgG antibody, as shown in Figure Q10). Figure Q10) The most likely candidate for cytokine 'X' is:
A) IFN-$\gamma$
B) IL-2
C) IL-4
D) IL-17
E) GM-CSF

Question

Toxoplasma gondii is a single-celled parasitic protozoan that infects and replicates in macrophages. It is common in the environment, and is transmitted to humans by the ingestion of undercooked meat or by accidental ingestion of the parasite's oocytes from contaminated water or cat litter. Infected individuals with healthy immune systems are generally asymptomatic, and rapidly clear the infection. However, in AIDS patients, infections of Toxoplasma gondii can lead to severe disease and even death. To investigate the immune mechanisms important in controlling Toxoplasma gondii, a mouse model of the infection was developed. Mice were infected with the protozoa at a dose where the majority of the mice survive the infection, and at the same time, were injected with a neutralizing antibody to a cytokine made by T cells (anti-'X' IgG). A second group of mice received the protozoa plus a control IgG antibody, as shown in Figure Q10).  Figure Q10) The most likely candidate for cytokine 'X' is:
A) IFN-$\gamma$ 
B) IL-2 
C) IL-4 
D) IL-17 
E) GM-CSF

Quizplus · Accepted Answer

IFN-γ is a cytokine produced by T cells that plays a critical role in the control of Toxoplasma gondii infection. Studies have shown that IFN-γ-deficient mice are highly susceptible to Toxoplasma gondii infection, while treatment with recombinant IFN-γ can improve control of the parasite. The fact that the anti-'X' antibody used in the study was a neutralizing antibody to a cytokine made by T cells suggests that the cytokine in question is likely to be IFN-γ. Therefore, choice A is the best choice. The other cytokines listed (IL-2, IL-4, IL-17, and GM-CSF) are not typically associated with control of Toxoplasma gondii infection, although they may play other roles in immune responses.

Toxoplasma Gondii Is a Single-Celled Parasitic Protozoan That Infects and Replicates